The U.S. National Highway Traffic Safety Administration states that nearly half of all traffic-related fatalities occur in the dark, despite only 25% of traffic traveling during darkness. Besides poor visibility and driver fatigue, the glare from headlight of oncoming traffic also makes the night time driving hazardous. As people age, the progress of cataract will make the glare even worse. However, there is little a driver can do except moving viewing direction away from the glare. By looking away, the driver will not be able to see the left curb or lane divider.
To reduce the hazard caused by headlight glare, government sets regulations on the beam pattern and the intensity of headlights. Government may also require drivers to turn off high beam when approaching other vehicles. However, there are still cars on the road not fully conforming to government regulations. The increase use of HID headlamps makes the glare more serious. Even if all cars meet government regulations, there can be still difficulty to drivers with certain vision deficiency or when the road condition is unfavorable.
The automobile industry has perfected visors to mitigate Sun glare for daylight driving. However, the Sun visor system cannot be transformed directly into a night time visor to reduce glare from headlights of oncoming vehicles. The reason is simple: the Sun is above in the sky and there is nothing near the Sun you need to see while in the case of headlight glare, you do need to see many objects around the headlight beam including the vehicle whose headlight is shining on you. If you use an opaque visor to block the headlight, you block objects you need to see around it.
Inventors attempted to mitigate this problem with various designs. There were basically six types of glare reduction methods cited in the US patent database. The first type is to improve headlamps by control of its intensity or beam width to reduce glare to other vehicles (U.S. Pat. No. 7,537,365 Bender, Glare reducing enhancements for vehicle exterior lighting systems and U.S. Pat. No. 6,515,425 Bender, Headlight anti-glare system). Such systems need government regulations to require every vehicle to install such system. The second type is to control the transparency of a pair of glasses worn by the driver or transparency of window glass to partially reduce the light to driver's eyes (U.S. Pat. No. 8,140,219 Cernasov, Automatic glare reduction system for vehicles; U.S. Pat. No. 8,143,563B2 Broude, Enhanced glare reduction and U.S. Pat. No. 6,575,569 Castellano, Headlight glare reducing ophthalmic lens system). Such methods will dim objects in the neighborhood as well. The third method is to use a small movable visor or semitransparent visor playing similar role as a Sun visor during the day (U.S. Pat. No. 6,318,787 Fahy, Automobile glare visor and U.S. Pat. No. 4,818,011 Cherian, Anti-glare visor system). Such method may also block neighborhood. The fourth one uses a sensor to detect glare intensity then increase intensity of own light to make the viewing field “homogeneous” (U.S. Pat. No. 6,568,738 Braun, Optical glare limiter). It reduces the “blinding effect” but the driver still cannot see objects clearly. The fifth is to require vehicles to polarize headlights in a fixed direction and let drivers to wear glasses polarized in perpendicular direction (U.S. Pat. No. 6,646,801 Sley, Glare Reduction System and Method). This obviously reduces the headlight glare but the driver will have difficulty to see objects illuminated by his/her own headlights because they are polarized in the same direction as other vehicles. The sixth requires both vehicles to install LCF on headlamps and windscreen. By detecting the other vehicle's phase and let the windshield LCF to be darkened during the bright phase of the other vehicle's light to reduce glare (US patent Application 20120126099 Tewari, Method for Reducing Glare from Light Source Through Windscreens). The requirement of both vehicles to install such system is not very practical. The presence of a third vehicles will pose problem. The patent does have a portion to deal with other cases with a complex method to darken certain area on the windshield between driver eyes and glare source by detecting the location of light source and driver eye position. The whole system is very complex.
To compare and evaluate diverse methods, we need some universal criteria. For a glare reduction system to be effective and practical, it has to meet the following three basic requirements: 1. It must work independently, meaning there is no need for other vehicle to make any change such as to require all other vehicles to install certain headlamps. 2. It must be anonymous, meaning other vehicle will not notice any change in the vehicle with the device installed. 3. It must not be self defeating, meaning the installed device shall not impede the original function of current installed equipment, especially headlamps. In other words, the objects being illuminated by own headlights shall not be dimmed. So far we have not found any patent, approved or in process, satisfying all three requirements.